The present invention relates to a multi-phase alternating-current rotational electric machine which controls multi-phase alternating currents by semiconductor switching devices, such as MOSFETs, IGBTs, and so on.
As the electric power load requirement increases because automobiles are becoming larger and up-graded, the demand for highly efficient and powerful automobile alternators (alternating-current generator for automobiles) is also increasing. With respect to the increased efficiency, according to the method disclosed in Japanese Patent Publication No. 2959640, the use of a MOSFET as a rectifying device reduces power losses (heat generation) more than the use of a conventional diode. With respect to high power, by mounting in parallel low power loss and low resistance MOSFETs, it is possible to rectify larger currents than the conventional method.
Especially for a rotational electric machine for automobiles, such as the above-mentioned alternator, the configuration that incorporates a power converting circuit unit into a rotational electric machine's main body (hereafter, referred to as “integral construction”) is highly desirable in terms of reduction in size, weight, and cost.
However, because the rotational electric machine's main body is mounted close to the engine and exposed to extreme thermal conditions, many examples of a conventional integral alternator, which uses silicon diodes that are resistant to relatively high temperatures, have been disclosed, but only one example (Japanese Laid-open Patent Publication No. Hei 8-331818) of a conventional integral alternator, which uses SiC (silicon carbide) devices that are resistant to higher temperature compared to the silicon devices, has been disclosed. Below are detailed descriptions of problems to be solved for achieving a highly efficient, powerful, integral rotational electric machine that incorporates silicon switching devices (MOSFETs, IGBTS, and so on).